Another important role of bone is its metabolic activity (calcium household, blood formation in red bone marrow).

Cartilage tissue

Cartilage tissue is mainly to be found in the skeleton and the respiratory tracts. It is composed of cartilage cells (chondrocytes), located in small groups within a basic cartilaginous substance (extracellular matrix).

Depending on the type and quantity of the fibers, a difference is made between elastic cartilage, hyaline cartilage and fibrous cartilage. Cartilage is supplied with nutrients either through the joint fluid or via the perichondrium. Cartilage is able to withstand extreme pressure and is very resistant. Cartilage, primarily to be found in the skeleton and the respiratory tracts, is firm, yet reacts elastically to pressure and bending. This is made possible by the matrix of cartilage (intercellular substance) which, together with the cartilaginous cells, forms the cartilaginous tissue. Depending on the ratio between the matrix of cartilage and cartilaginous cells, a distinction is made between hyaline cartilage, fibrous cartilage and elastic cartilage.

Cartilaginous cells are usually fairly round and to be found in groups within the matrix. The matrix of cartilage is 70% water, the rest consists of bundles of fibers with collagen, protein and elastin. Cartilage is supplied through the perichondrium or through synovia ("joint fluid"). As life goes on, the supply of nutrients diminishes, which can lead to wear and tear of the joints (arthrosis).

Hyaline cartilage is blueish in color and looks milky and glassy. It is especially to be found at the end of bones where joints are formed. It is also to be found in the ribs as costal cartilage and as laryngeal cartilage.

Fibrous cartilage consists of a network of numerous strong little fibers. It is highly tensile and may be found in menisci, intervertebral disks and in the pubic symphysis.

Elastic cartilage is yellowish in color. Its intercellular substance contains numerous elastic fibers which lend it its flexibility and elasticity. Elastic cartilage may be found in the region of the epiglottis and the auricle.

Bone Construction

In addition to the predominating bone tissue, lipogenic and hematogenic tissue may be found in the bone marrow region, tense connective tissue on the periosteum, cartilage in the growth zones and the epiphyses, and elastic connective tissue in the walls of the blood vessels. Bone is supplied by nerves.

Where an epiphysis (end of a joint) is missing, the bones are completely surrounded by the periosteum, consisting of two layers: one osteogenous (bone-forming) layer is located directly on top of the bone.

During the growth phase, it receives numerous osteogenous cells (osteoblasts), which then diminish in adults, not reappearing until a bone is broken and renewed cell formation is required. The outer layer of the periosteum consists of a network of high-tensile fibers, anchoring it directly to the bone. It serves to secure tendons, muscles and ligaments. The periosteum is supplied by blood vessels, lymph vessels and nerves. Bone - with the exception of dentin is the hardest substance within the human body.

Bone Formation

Bone formation (osteogenesis) can take place in one of two different ways. Either the bone develops directly from connective tissue, as for example with the flat skull bone or the bones forming the facial part of the skull, or the bone replaces cartilage at the ends of the long tubular bones following the growth phase and especially during it. Here a growth symphysis is located between the shaft and the end of the bone. Cartilage is reduced in both directions and replaced by bone tissue. At the same time new cartilage is formed, however, permitting lengthwise growth. Outwards growth takes place through the periosteum and throughout life.

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